Solid electrolytic capacitor with facedown terminations

ABSTRACT

A solid electrolytic capacitor that contains a capacitor element that includes an anode body, dielectric layer, and solid electrolyte is provided. The capacitor also contains an anode lead that is electrically connected to the anode body by a refractory metal paste (e.g., tantalum paste). The use of such a refractory metal paste allows the anode lead to be sinter bonded to a surface of the anode body after it is pressed. In this manner, a strong and reliable connection may be achieved without substantially decreasing the surface area of the lead that is available for connection to a termination. Furthermore, because the lead is not embedded within the anode body, the capacitor may be configured so that little, if any, portion of the lead extends beyond the anode body. This may result in a highly volumetrically efficient capacitor with excellent electrical properties.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) have been amajor contributor to the miniaturization of electronic circuits and havemade possible the application of such circuits in extreme environments.Conventional solid electrolytic capacitors are often formed by pressinga metal powder (e.g., tantalum) around a lead wire, sintering thepressed part, anodizing the sintered anode, and thereafter applying asolid electrolyte. The resulting capacitor element contains an anodelead that extends outwardly from the anode body and is electricallyconnected at its end to an anode termination. Similarly, the cathode iselectrically connected to a cathode termination. In certain cases, aportion of the anode termination is then bent around the capacitorcasing into a “J-shaped” configuration such that it is present on theend of the capacitor. When a number of these capacitors are mounted on aboard in a side-by-side fashion, however, the spacing must be made largeenough to prevent short-circuiting, which prevents dense packing of thecapacitors. Capacitors have been developed in which the terminations arelocated primarily on the bottom of the capacitor—also known as“facedown” terminations. Despite the benefits achieved, however, a needfor improvement still remains.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that comprises a capacitor elementthat includes an anode body, a dielectric layer overlying at least aportion of the anode body, and a cathode overlying at least a portion ofthe dielectric layer, the cathode including a solid electrolyte. Ananode lead is electrically connected to a surface of the anode body by arefractory metal paste, wherein the refractory metal paste is sinterbonded to both the anode lead and the anode body. An anode terminationis electrically connected to the anode lead, wherein the anodetermination contains a first component that is generally parallel to afirst surface of the capacitor element. A cathode termination iselectrically connected to the cathode, wherein the cathode terminationcontains a second component that is generally parallel to the firstsurface of the capacitor element. A case encapsulates the capacitorelement and leaves exposed at least a portion of the first component andthe second component.

In accordance with another embodiment of the present invention, a methodfor forming a solid electrolytic capacitor is disclosed. The methodcomprises forming a capacitor element by a method that comprisespressing an anode body; applying a refractory metal paste to a surfaceof the pressed anode body; positioning an anode lead adjacent to therefractory metal paste; sintering the anode body and the refractorymetal paste to electrically connect the anode lead to the anode body;anodically oxidizing at least a portion of the anode body to form adielectric layer; and forming a solid electrolyte over at least aportion of the dielectric layer. An anode termination is electricallyconnected to the anode lead, wherein the anode termination contains afirst component that is generally parallel to a first surface of thecapacitor element. A cathode termination is electrically connected tothe cathode, wherein the cathode termination contains a second componentthat is generally parallel to the first surface of the capacitorelement. The capacitor is encapsulated so that at least a portion of thefirst component and the second component remain exposed.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a cross-sectional view of one embodiment of the solidelectrolytic capacitor of the present invention;

FIG. 2 is a perspective view of one embodiment of an anode bodyconnected to an anode lead through a refractory metal paste;

FIG. 3 is a cross-sectional, exploded view of the anode body and leadshown in FIG. 2; and

FIG. 4 is a cross-sectional view of another embodiment of the solidelectrolytic capacitor of the present invention.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention.

Generally speaking, the present invention is directed to a solidelectrolytic capacitor that contains a capacitor element that includesan anode body, dielectric layer, and solid electrolyte. The capacitoralso contains an anode lead that is electrically connected to the anodebody by a refractory metal paste (e.g., tantalum paste). The use of sucha refractory metal paste allows the anode lead to be sinter bonded to asurface of the anode body after it is pressed. In this manner, a strongand reliable connection may be achieved without substantially decreasingthe surface area of the lead that is available for connection to atermination. Furthermore, because the lead is not embedded within theanode body, the capacitor may be configured so that little, if any,portion of the lead extends beyond the anode body. This may result in ahighly volumetrically efficient capacitor with excellent electricalproperties.

The anode body may be formed from a valve metal composition having ahigh specific charge, such as about 40,000 μF*V/g or more, in someembodiments about 50,000 μF*V/g or more, in some embodiments about60,000 μF*V/g or more, and in some embodiments, from about 70,000 toabout 700,000 μF*V/g. The valve metal composition contains a valve metal(i.e., metal that is capable of oxidation) or valve metal-basedcompound, such as tantalum, niobium, aluminum, hafnium, titanium, alloysthereof, oxides thereof, nitrides thereof, and so forth. For example,the valve metal composition may contain an electrically conductive oxideof niobium, such as niobium oxide having an atomic ratio of niobium tooxygen of 1:1.0±1.0, in some embodiments 1:1.0±0.3, in some embodiments1:1.0±0.1, and in some embodiments, 1:1.0±0.05. For example, the niobiumoxide may be NbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. In a preferredembodiment, the composition contains NbO_(1.0), which is a conductiveniobium oxide that may remain chemically stable even after sintering athigh temperatures. Examples of such valve metal oxides are described inU.S. Pat. No. 6,322,912 to Fife; U.S. Pat. No. 6,391,275 to Fife et al.;U.S. Pat. No. 6,416,730 to Fife et al.; U.S. Pat. No. 6,527,937 to Fife;U.S. Pat. No. 6,576,099 to Kimmel, et al.; U.S. Pat. No. 6,592,740 toFife, et al.; and U.S. Pat. No. 6,639,787 to Kimmel, et al.; and U.S.Pat. No. 7,220,397 to Kimmel, et al., as well as U.S. Patent ApplicationPublication Nos. 2005/0019581 to Schnitter; 2005/0103638 to Schnitter,et al.; 2005/0013765 to Thomas, et al., all of which are incorporatedherein in their entirety by reference thereto for all purposes.

Conventional fabricating procedures may generally be utilized to formthe anode body in one embodiment, a tantalum or niobium oxide powderhaving a certain particle size is first selected. For example, theparticles may be flaked, angular, nodular, and mixtures or variationsthereof. The particles also typically have a screen size distribution ofat least about 60 mesh, in some embodiments from about 60 to about 325mesh, and in some embodiments, from about 100 to about 200 mesh.Further, the specific surface area is from about 0.1 to about 10.0 m²/g,in some embodiments from about 0.5 to about 5.0 m²/g, and in someembodiments, from about 1.0 to about 2.0 m²/g. The term “specificsurface area” refers to the surface area determined by the physical gasadsorption (B.E.T.) method of Bruanauer, Emmet, and Teller, Journal ofAmerican Chemical Society, Vol. 60, 1938, p. 309, with nitrogen as theadsorption gas. Likewise, the bulk (or Scott) density is typically fromabout 0.1 to about 5.0 g/cm³, in some embodiments from about 0.2 toabout 4.0 g/cm³, and in some embodiments, from about 0.5 to about 3.0g/cm³.

To facilitate the construction of the anode body, other components maybe added to the electrically conductive particles. For example, theelectrically conductive particles may be optionally mixed with a binderand/or lubricant to ensure that the particles adequately adhere to eachother when pressed to form the anode body. Suitable binders may includecamphor, stearic and other soapy fatty acids, Carbowax (Union Carbide),Glyptal (General Electric), naphthalene, vegetable wax, microwaxes(purified paraffins), polymer binders (e.g., polyvinyl alcohol,polyethyl-2-oxazoline, etc), and so forth. The binder may be dissolvedand dispersed in a solvent. Exemplary solvents may include water,alcohols, and so forth. When utilized, the percentage of binders and/orlubricants may vary from about 0.1% to about 8% by weight of the totalmass. It should be understood, however, that binders and lubricants arenot required in the present invention.

The resulting powder may be compacted using any conventional powderpress mold. For example, the press mold may be a single stationcompaction press using a die and one or multiple punches. Alternatively,anvil-type compaction press molds may be used that use only a die andsingle lower punch. Single station compaction press molds are availablein several basic types, such as cam, toggle/knuckle and eccentric/crankpresses with varying capabilities, such as single action, double action,floating die, movable platen, opposed ram, screw, impact, hot pressing,coining or sizing. If desired, any binder/lubricant may be removed aftercompression by heating the pellet under vacuum at a certain temperature(e.g., from about 150° C. to about 500° C.) for several minutes.Alternatively, the binder/lubricant may also be removed by contactingthe pellet with an aqueous solution, such as described in U.S. Pat. No.6,197,252 to Bishop, et al., which is incorporated herein in itsentirety by reference thereto for all purposes.

The thickness of the pressed anode body may be relatively thin, such asabout 4 millimeters or less, in some embodiments, from about 0.05 toabout 2 millimeters, and in some embodiments, from about 0.1 to about 1millimeter. The shape of the anode body may also be selected to improvethe electrical properties of the resulting capacitor. For example, theanode body may have a shape that is curved, sinusoidal, rectangular,U-shaped, V-shaped, etc. The anode body may also have a “fluted” shapein that it contains one or more furrows, grooves, depressions, orindentations to increase the surface to volume ratio to minimize ESR andextend the frequency response of the capacitance. Such “fluted” anodesare described, for instance, in U.S. Pat. No. 6,191,936 to Webber, etal.; U.S. Pat. No. 5,949,639 to Maeda, et al.; and U.S. Pat. No.3,345,545 to Bourgault et al., as well as U.S. Patent ApplicationPublication No. 2005/0270725 to Hahn, et al., all of which areincorporated herein in their entirety by reference thereto for allpurposes.

Regardless of its particular configuration, the pressed anode body isattached to an anode lead using a refractory metal paste. The pastegenerally contains particles of a relatively small size, such as havingan average size of from about 0.01 to about 20 micrometers, in someembodiments from about 0.1 to about 15 micrometers, and in someembodiments, from about 1 to about 10 micrometers. Due to in part to therelatively small size of the particles, the paste may have a relativelylow viscosity, allowing it to be readily handled and applied to an anodelead and/or anode body during manufacture of the capacitor. Theviscosity may, for instance, range from about 5 to about 200Pascal-seconds, in some embodiments from about 10 to about 150Pascal-seconds, and in some embodiments, from about 20 to about 100Pascal-seconds, as measured with a Brookfield DV-1 viscometer usingSpindie No. 18 operating at 12 rpm and 25° C. if desired, thickeners orother viscosity modifiers may be employed in the paste to increase ordecrease viscosity. Further, the thickness of the applied paste may alsobe relatively thin and still achieve the desired binding of the lead tothe anode body. For example, the thickness of the paste may be fromabout 0.01 to about 50 micrometers, in some embodiments from about 0.5to about 30 micrometers, and in some embodiments, from about 1 to about25 micrometers.

The particles used in the paste are formed from a composition thatincludes a refractory metal, such as tungsten, molybdenum, niobium,tantalum, rhenium, osmium, iridium, ruthenium, hafnium, zirconium,vanadium, chromium, as well as electrically conductive alloys, oxides,and nitrides of these metals. Preferably, the composition is the same orsubstantially similar in nature to the material used to form the anodebody. In one particular embodiment, for example, tantalum metalparticles are employed for bonding to a tantalum anode.

To form the paste, the particles may be initially dispersed in asolvent. Any solvent of a variety of solvents may be employed, such aswater; glycols (e.g., propylene glycol, butylene glycol, triethyleneglycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, anddipropyleneglycol); glycol ethers (e.g., methyl glycol ether, ethylglycol ether, and isopropyl glycol ether); ethers (e.g., diethyl etherand tetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol,iso-propanol, and butanol); triglycerides; ketones (e.g., acetone,methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethylacetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth. One particular benefit ofthe present invention is that aqueous solvents (e.g., water) may beemployed. In fact, water may constitute about 20 wt. % or more, in someembodiments, about 50 wt. % or more, and in some embodiments, about 75wt. % to 100 wt. % of the solvent(s) used in the paste.

The total concentration of solvent(s) employed in the paste may vary,but is typically from about 1 wt. % to about 40 wt. %, in someembodiments from about 5 wt. % to about 30 wt. %, and in someembodiments, from about 10 wt. % to about 20 wt. % of the paste. Ofcourse, the specific amount of solvent(s) employed depends in part onthe desired solids content and/or viscosity of the paste. For example,the solids content may range from about 40% to about 98% by weight, moreparticularly, between about 50% to about 96% by weight, and even moreparticularly, between about 60% to about 95% by weight. By varying thesolids content of the paste, the presence of the refractory metalparticles may be controlled. For example, to form a paste with a higherlevel of particles, the formulation may be provided with a relativelyhigh solids content so that a greater percentage of the particles areincorporated into the paste.

The paste may also employ an adhesive to help retain the particles in anundisrupted position and/or assist in the adherence of the paste to thedesired surface. Although any adhesive may be employed, organicadhesives are particularly suitable for use in the present invention.Examples of such adhesives may include, for instance, epoxy compounds(e.g., two-component UHU epoxy adhesive); poly(vinyl butyral);poly(vinyl acetate); poly(vinyl alcohol); poly(vinyl pyrollidone);cellulosic polymers, such as carboxymethylcellulose, methyl cellulose,ethyl cellulose, hydroxyethyl cellulose, and methylhydroxyethylcellulose; atactic polypropylene, polyethylene; polyethylene glycol(e.g., Carbowax from Dow Chemical Co.); silicon polymers, such aspoly(methyl siloxane), poly(methylphenyl siloxane); polystyrene,poly(butadiene/styrene); polyamides, polyimides, and polyacrylamides,high molecular weight polyethers; copolymers of ethylene oxide andpropylene oxide; fluoropolymers, such as polytetrafluoroethylene,polyvinylidene fluoride, and fluoro-olefin copolymers; and acrylicpolymers, such as sodium polyacrylate, poly(lower alkyl acrylates),poly(lower alkyl methacrylates) and copolymers of lower alkyl acrylatesand methacrylates.

In addition to adhesives, the paste may also include other components.For example, one or more dispersants may be employed in the paste toreduce the surface tension of the suspension. One class of suitabledispersants includes anionic compounds having acid groups or saltsthereof. Such compounds, for example, may contain at least oneethylenically unsaturated acid containing monomer and optionally atleast one ethylenically unsaturated nonionic monomer. Suitable acidmonomers include monomers having carboxylic acid groups, such as acrylicacid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid,maleic acid, monomethyl itaconate, monomethyl fumarate, and monobutylfumarate; anhydrides, such as maleic anhydride and itaconic anhydride;or combinations thereof. Suitable ethylenically unsaturated monomersinclude alkyl esters of (meth)acrylic acid, such as ethyl acrylate,butyl acrylate, and methyl methacrylate; hydroxy esters of (meth)acrylicacid, such as hydroxyethyl methacrylate, hydroxyethyl acrylate,hydroxypropyl acrylate, and hydroxypropyl methacrylate; aromaticmonomers, such as styrene and α-methyl styrene; and alkenes, such asdi-isobutylene.

A wetting agent, or surfactant, may also be employed in the paste tofacilitate the formation of homogeneously uniform pastes havingdesirable spreadability. Suitable surfactants may include cationicsurfactants, nonionic surfactants, anionic surfactants, amphotericsurfactants, and so forth. Nonionic surfactants, for instance, may havea hydrophobic base, such as a long chain alkyl group or an alkylatedaryl group, and a hydrophilic chain comprising a certain number (e.g., 1to about 30) of ethoxy and/or propoxy moieties. Examples of some classesof nonionic surfactants that can be used include, but are not limitedto, ethoxylated alkylphenols, ethoxylated and propoxylated fattyalcohols, polyethylene glycol ethers of methyl glucose, polyethyleneglycol ethers of sorbitol, ethylene oxide-propylene oxide blockcopolymers, ethoxylated esters of fatty (C₈-C₁₈) acids, condensationproducts of ethylene oxide with long chain amines or amides,condensation products of ethylene oxide with alcohols, and mixturesthereof. Particularly suitable nonionic surfactants may include thepolyethylene oxide condensates of one mole of alkyl phenol containingfrom about 8 to 18 carbon atoms in a straight- or branched-chain alkylgroup with about 5 to 30 moles of ethylene oxide. Specific examples ofalkyl phenol ethoxylates include nonyl condensed with about 9.5 moles ofethylene oxide per mole of nonyl phenol, dinonyl phenol condensed withabout 12 moles of ethylene oxide per mole of phenol, dinonyl phenolcondensed with about 15 moles of ethylene oxide per mole of phenol anddiisoctylphenol condensed with about 15 moles of ethylene oxide per moleof phenol.

Plasticizers may also be employed in the paste to enhance thefilm-forming characteristics of the paste. Plasticizers are well-knownand a wide range of plasticizers can be employed. Examples of typicalplasticizers include mineral oil; glycols, such as propylene glycol;phthalic esters, such as dioctyl phthalate and benzyl butyl phthalate;and long-chain aliphatic acids, such as oleic acid and stearic acid; andmixtures thereof.

The concentration of each component of the paste may vary depending onthe amount of particles desired, the wet pick-up of the applicationmethod utilized, etc. For example, the amount of the particles withinthe paste generally ranges from about 40 wt. % to about 98 wt. %, insome embodiments from about 50 wt. % to about 96 wt. %, and in someembodiments, from about 60 wt. % to about 95 wt. %. Adhesive(s) may alsoconstitute from about 0.01 wt. % to about 20 wt. %, in some embodimentsfrom about 0.1 wt. % to about 15 wt. %, and in some embodiments, fromabout 1 wt. % to about 10 wt. % of the paste. Other components, such asdispersants, surfactants, plasticizers, etc., may each constitute fromabout 0.001 wt. % to about 10 wt. %, in some embodiments from about 0.01wt. % to about 5 wt. %, and in some embodiments from about 0.1 wt. % toabout 3 wt. % of the paste.

As indicated above, the refractory metal paste of the present inventionis used to electrically connect the anode body of a solid electrolyticcapacitor to the anode lead. The anode lead may be in the form of aribbon, wire, sheet, etc., and may be formed from a valve metal, such astantalum, niobium, niobium oxide, etc.

Any of a variety of techniques may generally be employed to apply therefractory metal paste, such as heat treating, thermal sintering,sputtering, screen-printing, dipping, electrophoretic coating, electronbeam deposition, spraying, roller pressing, brushing, doctor bladecasting, vacuum deposition, coating, etc. The paste may also be appliedto any surface of the anode body and/or lead. Referring to FIG. 2, forexample, one embodiment is shown in which an anode lead 16 is connectedto an upper surface 33 of an anode body 12. Of course, the anode lead 16may also be connected one or more other surfaces of the anode body 12,such as side surface 35, side surface 37, front surface 31, bottomsurface 39, and/or rear surface (not shown). If desired, the anode bodymay also contain a recessed region to accommodate the shape of the anodelead. In FIG. 2, for example, a recessed region 43 is defined in thesurface 33 of the anode body 12 that has a “U-shape” for accommodatingthe generally circular-shaped anode lead 16.

Once applied, the refractory metal paste may be optionally heated toremove any adhesive/lubricant present. Regardless, the paste is sinteredso that the particles of the paste form a bond with both the anode leadand anode body. Sintering of the paste in accordance with the presentinvention may occur before and/or after the anode body is sintered. Inone particular embodiment, the refractory metal paste is co-sinteredwith the anode body. The temperature at which the paste is sintered mayrange, for example, from about 1000° C. to about 2500° C., in someembodiments from about 1000° C. to about 2000° C., and in someembodiments from about 1200° C. to about 1800° C. Sintering may occur atany desired pressure. In certain embodiments, sintering may occur at arelatively low pressure, such as less than about 200 millitorr, in someembodiments less than about 100 millitorr, and in some embodiments, lessthan about 50 millitorr. The total time of sintering may also range fromabout 10 minutes to about 1 hour.

As indicated above, sintering causes a bond to form between theparticles of the refractory metal paste and the metal of both the anodebody and the anode lead. Contrary to conventional capacitors, a strongconnection may thus be achieved between the anode lead and anode bodywithout embedding the lead into the body. Because it is not embeddedwithin the anode body, a significant portion of the surface area of theanode lead can remain available for subsequent bonding to an anodetermination. This, in turn, means that the anode lead does not need toextend outwardly beyond the anode body for attaching to the termination.In this regard, only a small portion, if any, of the anode lead mayextend outwardly beyond the anode body. Referring again to FIG. 2, forinstance, the anode lead 16 of this embodiment generally extends in alongitudinal direction along the −y axis. The length that the anode lead16 extends in the −y direction beyond the front surface 31 or the rearsurface (not shown) is generally kept small to optimize volumetricefficiency. For example, although the actual lengths may vary dependingon the case size of the capacitor, the ratio of the distance that thelead 16 extends beyond a surface of the anode body in the longitudinaldirection to the length of the anode body in the same direction istypically about 0.5 or less, in some embodiments about 0.1 or less, andin some embodiments, from about 0.001 to about 0.05. The desired lengthof the anode lead may be achieved by simply selecting a lead with theappropriate length, or by cutting the lead to the desired length afterit is attached in addition to optional cutting steps, the lead may alsobe ground so that it possesses a relatively flat surface for subsequentconnection to an anode termination.

In the embodiments described above, the refractory metal paste directlycontacts the anode body and lead. Nevertheless, it should be understoodthat one or more materials may also be employed between the paste andthe component(s) to assist in the connection. For example, a layer ofseed particles (not in the form of a paste) may be disposed between thepaste and anode body to improve adhesion. Such seed layer particles mayinclude a valve metal material (e.g., tantalum) such as described above.

Once attached to the lead, the anode body may be anodized so that adielectric layer is formed over and/or within the anode. Anodization isan electrochemical process by which the anode is oxidized to form amaterial having a relatively high dielectric constant. For example, atantalum anode may be anodized to tantalum pentoxide (Ta₂O₅). Typically,anodization is performed by initially applying an electrolyte to theanode, such as by dipping anode into the electrolyte. The electrolyte isgenerally in the form of a liquid, such as a solution (e.g., aqueous ornon-aqueous), dispersion, melt, etc. A solvent is generally employed inthe electrolyte, such as water (e.g., deionized water); ethers (e.g.,diethyl ether and tetrahydrofuran); alcohols (e.g., methanol, ethanol,n-propanol, isopropanol, and butanol); triglycerides; ketones (e.g.,acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g.,ethyl acetate, butyl acetate, diethylene glycol ether acetate, andmethoxypropyl acetate); amides (e.g., dimethylformamide,dimethylacetamide, dimethylcaprylic/capric fatty acid amide andN-alkylpyrrolidones); nitriles (e.g., acetonitrile, propionitrile,butyronitrile and benzonitrile); sulfoxides or sulfones (e.g., dimethylsulfoxide (DMSO) and sulfolane); and so forth. The solvent mayconstitute from about 50 wt. % to about 99.9 wt. %, in some embodimentsfrom about 75 wt. % to about 99 wt. %, and in some embodiments, fromabout 80 wt. % to about 95 wt. % of the electrolyte. Although notnecessarily required, the use of an aqueous solvent (e.g., water) isoften desired to help achieve the desired oxide. In fact, water mayconstitute about 50 wt. % or more, in some embodiments, about 70 wt. %or more, and in some embodiments, about 90 wt. % to 100 wt. % of thesolvent(s) used in the electrolyte.

The electrolyte is ionically conductive and may have an ionicconductivity of about 1 milliSiemens per centimeter (“mS/cm”) or more,in some embodiments about 30 mS/cm or more, and in some embodiments,from about 40 mS/cm to about 100 mS/cm, determined at a temperature of25° C. To enhance the ionic conductivity of the electrolyte, a compoundmay be employed that is capable of dissociating in the solvent to formions. Suitable ionic compounds for this purpose may include, forinstance, acids, such as hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.;organic acids, including carboxylic acids, such as acrylic acid,methacrylic acid, malonic acid, succinic acid, salicylic acid,sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid,gallic acid, tartaric acid, citric acid, formic acid, acetic acid,glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalicacid, glutaric acid, gluconic acid, lactic acid, aspartic acid,glutaminic acid, itaconic acid, trifluoroacetic acid, barbituric acid,cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid,etc.; sulfonic acids, such as methanesulfonic acid, benzenesulfonicacid, toluenesulfonic acid, trifluoromethanesulfonic acid,styrenesulfonic acid, naphthalene disulfonic acid,hydroxybenzenesulfonic acid, dodecylsulfonic acid,dodecylbenzenesulfonic acid, etc.; polymeric acids, such aspoly(acrylic) or poly(methacrylic) acid and copolymers thereof (e.g.,maleic-acrylic, sulfonic-acrylic, and styrene-acrylic copolymers),carageenic acid, carboxymethyl cellulose, alginic acid, etc.; and soforth. The concentration of ionic compounds is selected to achieve thedesired ionic conductivity. For example, an acid (e.g., phosphoric acid)may constitute from about 0.01 wt. % to about 5 wt. %, in someembodiments from about 0.05 wt. % to about 0.8 wt. %, and in someembodiments, from about 0.1 wt. % to about 0.5 wt. % of the electrolyte.If desired, blends of ionic compounds may also be employed in theelectrolyte.

A current is passed through the electrolyte to form the dielectriclayer. The value of voltage manages the thickness of the dielectriclayer. For example, the power supply may be initially set up at agalvanostatic mode until the required voltage is reached. Thereafter,the power supply may be switched to a potentiostatic mode to ensure thatthe desired dielectric thickness is formed over the surface of theanode. Of course, other known methods may also be employed, such aspulse or step potentiostatic methods. The voltage typically ranges fromabout 4 to about 200 V, and in some embodiments, from about 9 to about100 V. During anodic oxidation, the electrolyte can be kept at anelevated temperature, such as about 30° C. or more, in some embodimentsfrom about 40° C. to about 200° C., and in some embodiments, from about50° C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode and within its pores.

The anodized part may be subjected to a step for forming a cathode thatincludes a solid electrolyte, such as a manganese dioxide, conductivepolymer, etc. A manganese dioxide solid electrolyte may, for instance,be formed by the pyrolytic decomposition of manganous nitrate(Mn(NO₃)₂). Such techniques are described, for instance, in U.S. Pat.No. 4,945,452 to Sturmer, et al., which is incorporated herein in itsentirety by reference thereto for all purposes. Alternatively, aconductive polymer coating may be employed that contains one or morepolyheterocycles (e.g., polypyrroles; polythiophenes,poly(3,4-ethylenedioxythiophene) (PEDT); polyanilines); polyacetylenes;poly-p-phenylenes; polyphenolates; and derivatives thereof. Moreover, ifdesired, the conductive polymer coating may also be formed from multipleconductive polymer layers. For example, in one embodiment, theconductive polymer cathode may contain one layer formed from PEDT andanother layer formed from a polypyrrole. Various methods may be utilizedto apply the conductive polymer coating onto the anode part. Forinstance, conventional techniques such as electropolymerization,screen-printing, dipping, electrophoretic coating, and spraying, may beused to form a conductive polymer coating. In one embodiment, forexample, the monomer(s) used to form the conductive polymer (e.g.,3,4-ethylenedioxy-thiophene) may initially be mixed with apolymerization catalyst to form a solution. For example, one suitablepolymerization catalyst is CLEVIOS C, which is iron IIItoluene-sulfonate and sold by H. C. Starck. CLEVIOS C is a commerciallyavailable catalyst for CLEVIOS M, which is 3,4-ethylene dioxythiophene,a PEDT monomer also sold by H. C. Starck. Once a catalyst dispersion isformed, the anode part may then be dipped into the dispersion so thatthe polymer forms on the surface of the anode part. Alternatively, thecatalyst and monomer(s) may also be applied separately to the anodepart. In one embodiment, for example, the catalyst may be dissolved in asolvent (e.g., butanol) and then applied to the anode part as a dippingsolution. The anode part may then be dried to remove the solventtherefrom. Thereafter, the anode part may be dipped into a solutioncontaining the appropriate monomer. Once the monomer contacts thesurface of the anode part containing the catalyst, it chemicallypolymerizes thereon. Techniques, such as described above, may bedescribed in more detail in U.S. Publication No. 2008/232037 to Biler.

In addition, the catalyst (e.g., CLEVIOS C) may also be mixed with thematerial(s) used to form the optional protective coating (e.g., resinousmaterials). In such instances, the anode part may then be dipped into asolution containing the monomer (CLEVIOS M). As a result, the monomercan contact the catalyst within and/or on the surface of the protectivecoating and react therewith to form the conductive polymer coating.Techniques, such as described above, may be described in more detail inU.S. Pat. No. 7,460,358 to Biler. Although various methods have beendescribed above, it should be understood that any other method forapplying the conductive coating(s) to the anode part may also beutilized in the present invention. For example, other methods forapplying such conductive polymer coating(s) may be described in U.S.Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 to Sakata,et al., U.S. Pat. No. 5,729,428 to Sakata, et al., and U.S. Pat. No.5,812,367 to Kudoh, et al., which are incorporated herein in theirentirety by reference thereto for all purposes.

Once applied, the solid electrolyte may be healed. Healing may occurafter each application of a solid electrolyte layer or may occur afterthe application of the entire coating. In some embodiments, for example,the solid electrolyte may be healed by dipping the pellet into anelectrolyte solution, such as a solution of acid, and thereafterapplying a constant voltage to the solution until the current is reducedto a preselected level. If desired, such healing may be accomplished inmultiple steps. After application of some or all of the layers describedabove, the pellet may then be washed if desired to remove variousbyproducts, excess catalysts, and so forth. Further, in some instances,drying may be utilized after some or all of the dipping operationsdescribed above. For example, drying may be desired after applying thecatalyst and/or after washing the pellet in order to open the pores ofthe pellet so that it can receive a liquid during subsequent dippingsteps.

If desired, the part may optionally be applied with a carbon layer(e.g., graphite) and silver layer, respectively. The silver coating may,for instance, act as a solderable conductor, contact layer, and/orcharge collector for the capacitor and the carbon coating may limitcontact of the silver coating with the solid electrolyte. Such coatingsmay cover some or all of the solid electrolyte.

Generally speaking, it is desirable to electrically isolate the anodetermination from the cathode termination so that the capacitor functionsin the desired manner. To achieve such isolation, a variety oftechniques may be implemented. In one embodiment, for instance, anyoxide and/or cathode layer(s) formed on the lead may simply be removedthrough an etching process (e.g., chemical, laser, etc.). Likewise, aprotective coating may also be formed on the anodized porous body and/orthe anode lead, either prior to or after anodization, to protect it fromcontact with the solid electrolyte. Referring to FIG. 3, for example,one embodiment of an anode body 12 is shown that is electricallyconnected to an anode lead 16 via a refractory metal paste 80. In thisparticular embodiment, a protective coating 17 is disposed over theanode lead 16 to help isolate the anode lead from the cathode duringsubsequent processing steps, such as described above. When employed, thecoating may be insulative and have a specific resistivity of greaterthan about 10 Ω/cm, in some embodiments greater than about 100, in someembodiments greater than about 1,000 Ω/cm, in some embodiments greaterthan about 1×10⁵ Ω/cm, and in some embodiments, greater than about1×10¹⁰ Ω/cm. Examples of such insulative materials may include polymers,such as polyurethane, polystyrene, esters of unsaturated or saturatedfatty acids (e.g., glycerides), polytetrafluoroethylene (e.g., Teflon™),and so forth.

As indicated above, the electrolytic capacitor of the present inventionalso contains an anode termination to which the anode lead of thecapacitor element is electrically connected and a cathode termination towhich the cathode of the capacitor element is electrically connected.Any conductive material may be employed to form the terminations, suchas a conductive metal (e.g., copper, nickel, silver, nickel, zinc, tin,palladium, lead, copper, aluminum, molybdenum, titanium, iron,zirconium, magnesium, and alloys thereof). Particularly suitableconductive metals include, for instance, copper, copper alloys (e.g.,copper-zirconium, copper-magnesium, copper-zinc, or copper-iron),nickel, and nickel alloys (e.g., nickel-iron). The thickness of theterminations is generally selected to minimize the thickness of thecapacitor. For instance, the thickness of the terminations may rangefrom about 0.05 to about 1 millimeter, in some embodiments from about0.05 to about 0.5 millimeters, and from about 0.07 to about 0.2millimeters.

The terminations may be connected using any technique known in the art,such as welding, adhesive bonding, etc. In one embodiment, for example,a conductive adhesive may initially be applied to a surface of the anodeand/or cathode terminations. The conductive adhesive may include, forinstance, conductive metal particles contained with a resin composition.The metal particles may be silver, copper, gold, platinum, nickel, zinc,bismuth, etc. The resin composition may include a thermoset resin (e.g.,epoxy resin), curing agent (e.g., acid anhydride), and coupling agent(e.g., silane coupling agents). Suitable conductive adhesives may bedescribed in U.S. Patent Application Publication No. 2006/0038304 toOsako, et al., which is incorporated herein in its entirety by referencethereto for all purposes.

Once the capacitor element is attached, the lead frame is enclosedwithin a casing, which may then be filled with silica or any other knownencapsulating material. The width and length of the case may varydepending on the intended application. Suitable casings may include, forinstance, “A”, “B”, “F”, “G”, “H”, “J”, “K”, “L”, “M”, “N”, “P”, “R”,“S”, “T”, “W”, “Y”, or “X” cases (AVX Corporation). Regardless of thecase size employed, the capacitor element is encapsulated so that atleast a portion of the anode and cathode terminations are exposed. Theexposed portion of the anode and cathode terminations are generallylocated at the bottom surface of the capacitor in a “facedown”configuration for mounting onto a circuit board. This increases thevolumetric efficiency of the capacitor and likewise reduces itsfootprint on the circuit board. After encapsulation, exposed portions ofthe anode and cathode terminations may be aged, screened, and trimmed tothe desired size.

Referring to FIG. 1, one embodiment of an electrolytic capacitor 10 isshown that includes an anode termination 24 and a cathode termination 28in electrical connection with a capacitor element 13. The terminations24, 28 and the capacitor element 13 are encapsulated within a case 50 sothat the resulting capacitor 10 has an upper surface 73, side surfaces71 and 75, a lower surface 70, and front and rear surfaces (not shown).The capacitor element 13 likewise includes an anode body 12, dielectriclayer 116, and a cathode layer 14, and has an upper surface 33, lowersurface 39, side surfaces 35 and 37, and a rear surface (not shown).

The cathode termination 28 is electrically connected to the lowersurface 39 of the capacitor element 13 via a conductive adhesive 92. Theanode termination 24 is likewise electrically connected to the anodelead 16 via a conductive adhesive 90. Of course, it should be understoodthat any other known method for connecting the terminations may also beemployed in the present invention. In any event, the anode termination24 and the cathode termination portion 28 are generally parallel andcoplanar with one another and optionally with the lower surface 39 ofthe capacitor element 13. Exposed portions of the anode and cathodeterminations 24 and 28 define lower surfaces 83 and 93, respectively,that face away from the lower surface 39 of the capacitor element 13. Inthis manner, the lower surfaces 83 and 93 of the terminations may begenerally parallel and coplanar with a lower surface 70 of the capacitor10. Although not required, other portions of the anode termination 24and cathode termination 28 may also remain exposed after encapsulation.In FIG. 1, for instance, the terminations 24 and 28 are also exposed atside surfaces 71 and 75, respectively, of the case 50.

In the embodiment shown in FIG. 1, the anode lead 16 is electricallyconnected to a single anode termination 24. It should be understood,however, that the particular location position and location of the leadand/or terminations may vary depending on the desired result. Referringto FIG. 4, for example, a capacitor 100 is shown that includes acapacitor element 113, cathode termination 128, and an anode terminationdefined by a first component 124 a and a second component 124 b. In thisparticular embodiment, an anode lead 116 is connected to an anode body112 of the capacitor element 113 via a refractory metal paste 143 and tothe second component 124 b via a conductive adhesive 190. Likewise, thefirst component 124 a is connected to the capacitor element 113 via aconductive adhesive 193 and the cathode termination 128 is connected tothe capacitor element 113 via a conductive adhesive 192. By disposingthe anode lead 116 between two different terminations, as shown, therobustness of the resulting capacitor 100 may be improved.

The present invention may be better understood by reference to thefollowing examples.

Test Procedures

Equivalent Series Resistance (ESR), Capacitance, and Dissipation Factor:

Equivalence series resistance and impedance were measured using aKeithley 3330 Precision LCZ meter with Kelvin Leads with 0 volts biasand 1 volt signal. The operating frequency was 100 kHz. The capacitanceand dissipation factor were measured using a Keithley 3330 Precision LCZmeter with Kelvin Leads with 2 volts bias and 1 volt signal. Theoperating frequency was 120 Hz and the temperature was 23° C.±2° C.

Leakage Current:

Leakage current (“DCL”) was measured using a MC 190 Leakage test setmade by Mantracourt Electronics LTD, UK. The MC 190 test measuresleakage current at a temperature of 25° C. and at a certain ratedvoltage after 10 seconds.

Example 1

150,000 μFV/g tantalum powder was pressed into pellets with diameters of26.5×2.2×0.65 (length×width×thickness) and glued with a tantalum ribbonusing tantalum paste as described above. The powder was then sintered toform a porous electrode body. The pellets were anodized in a phosphoricacid electrolyte in water and subsequently shell formed inwater/ethylene glycol electrolyte to form the dielectric layer. Amanganese dioxide solid electrolyte was formed by the pyrolyticdecomposition of manganous nitrate (Mn(NO₃)₂). The pellets were thencoated with a graphite coating and a silver coating. The finished partswere completed by conventional assembly technology and measured.

Example 2

150,000 μFV/g tantalum powder was pressed into pellets and sintered toform a porous electrode body using conventional pressing technology. Thepellets were anodized in a phosphoric acid electrolyte in water andsubsequently shell formed in water/ethylene glycol electrolyte. Amanganese dioxide solid electrolyte was formed by the pyrolyticdecomposition of manganous nitrate (Mn(NO₃)₂). The pellets were thencoated with a graphite coating and a silver coating. The finished partswere completed by conventional assembly technology and measured.

The electrical properties of the samples made in Examples 1 and 2 werethen tested. The results are shown below in Table 1.

The electrical properties of the samples made in Examples 1 and 2 werethen tested. The results are shown below in Table 1.

TABLE 1 Leakage Cap DF ESR Current Capacitor (μF) (%) (mμ) (μA) Example1 154 5.1 195 1.2 Example 2 137 5.2 240 4.9

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A solid electrolytic capacitor comprising: a capacitor element that includes an anode body, a dielectric layer overlying at least a portion of the anode body, and a cathode overlying at least a portion of the dielectric layer, the cathode including a solid electrolyte, and wherein the anode body is a pressed porous pellet; an anode lead that is electrically connected to a surface of the anode body by a refractory metal paste, wherein the refractory metal paste is sinter bonded to both the anode lead and the anode body; an anode termination that is electrically connected to the anode lead, wherein the anode termination contains a first component that is generally parallel to a first surface of the capacitor element; a cathode termination that is electrically connected to the cathode, wherein the cathode termination contains a second component that is generally parallel to the first surface of the capacitor element, wherein the anode termination and cathode termination both extend primarily in a direction that is parallel to the first surface of the capacitor element, the anode and cathode terminations being electrically connected to the first surface of the capacitor element; and a case that encapsulates the entire capacitor element so that the capacitor has an upper surface and opposing lower surface, wherein the anode termination and the cathode termination are primarily encapsulated within the case except that at least a portion of the first component and the second component remain exposed by the case at the lower surface of the capacitor.
 2. The solid electrolytic capacitor of claim 1, wherein the anode body includes tantalum, niobium, or an electrically conductive oxide thereof.
 3. The solid electrolytic capacitor of claim 1, wherein the anode lead contains tantalum or niobium.
 4. The solid electrolytic capacitor of claim 1, wherein the refractory metal paste includes a plurality of particles.
 5. The solid electrolytic capacitor of claim 4, wherein the particles are formed from tantalum.
 6. The solid electrolytic capacitor of claim 4, wherein the particles have an average size of from about 0.01 to about 20 micrometers.
 7. The solid electrolytic capacitor of claim 1, wherein the paste has a thickness of from about 0.01 to about 50 micrometers.
 8. The solid electrolytic capacitor of claim 1, wherein the surface of the anode body defines a recessed region to which the anode lead is electrically connected.
 9. The solid electrolytic capacitor of claim 8, wherein the recessed region is generally U-shaped.
 10. The solid electrolytic capacitor of claim 1, wherein the anode lead extends in a longitudinal direction, further wherein the ratio of the distance that the anode lead extends beyond a surface of the anode body in the longitudinal direction to the length of the anode body in the longitudinal direction is about 0.5 or less.
 11. The solid electrolytic capacitor of claim 1, wherein the anode lead contains a protective coating that electrically isolates the anode termination from the cathode termination.
 12. The solid electrolytic capacitor of claim 1, wherein the solid electrolyte includes manganese dioxide or a conductive polymer.
 13. The solid electrolytic capacitor of claim 1, wherein the cathode termination is electrically connected to the first surface of the capacitor element.
 14. The solid electrolytic capacitor of claim 1, wherein the exposed portions of the first component and the second component are generally coplanar.
 15. The solid electrolytic capacitor of claim 1, wherein the exposed portions of the first component and the second component respectively define an upper surface facing a lower surface of the capacitor element and an opposing lower surface facing away from the lower surface of the capacitor element, wherein the lower surfaces of the first component and the second component are configured to be mounted to a circuit board.
 16. The solid electrolytic capacitor of claim 1, wherein a single refractory metal paste is used to electrically connect the anode lead to a surface of the anode body. 